In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such a hot process gas, often referred to as a flue gas, containing, among other components, carbon dioxide, CO2. The negative environmental effects of releasing carbon dioxide to the atmosphere have been widely recognized, and have resulted in the development of processes adapted for removing carbon dioxide from the hot process gas generated in the combustion of the above mentioned fuels.
US2008/0178733 presents a gas cleaning system having a combined cooling and cleaning system comprising a first gas-liquid contacting device located upstream of the CO2 absorber and operative for cooling the process gas by means of a cooling liquid, and for absorbing into the cooling liquid sulfur dioxide of the process gas, such that a cooling liquid containing sulfate is obtained. The combined cooling and cleaning system further comprises a second gas-liquid contacting device located downstream of the CO2 absorber and operative for removing ammonia from the process gas, which has been treated in the CO2 absorber, by means of bringing the process gas containing ammonia into contact with the cooling liquid containing sulfate.
The system described in US2008/0178733 may be used to achieve one or more of the following aims:                1) Reducing the temperature of the process gas before it is fed to the CO2 absorber,        2) Removing SO2 from the process gas before it is fed to the CO2 absorber,        3) Removing residual NH3 from the process gas before it is discharged to the atmosphere,        4) Reheating the cold process gas from the CO2 absorber to retain cold energy, thus reducing the overall cooling requirement of the system,However, several of these aims are opposing in nature. The variables available for optimizing the process in respect of these aims are coupled to each other to a large extent. This means that not all aims can be fulfilled simultaneously. Optimizing the process in respect of some aims will lead to poor results in respect of other aims.        
Therefore, it would be desirable to have a process which would allow all of these aims to be fulfilled simultaneously.